1. Field of the Invention
The present invention relates to a method of sending an alarm to a network management station when an unusual event occurs in one of a plurality of managed network stations in a wide area network (WAN). The present invention finds an extensive use in a wide area network such as a TCP/IP (transmission-control protocol/internet protocol) based network wherein a network delay is considerably large compared with a LAN (local area network). The present invention is able to effectively solve congestion problems of a conventional control path thereby achieving substantial savings of network capacity.
2. Description of the Related Art
It is known in the art that information that is useful for purposes of network controlling is collected and stored by each of a plurality of managed stations and made available to a network management station. The information stored in the managed stations are automatically sent in packets to the network management station via the control path. Thus, when unusual events occur in many managed stations essentially at the same time, there is a possibility that the control path may be congested.
In order to address such a problem, it is proposed to make use of a technique known as polling on demand. In more specific terms, when an alarm is generated in a given managed station, the managed station issues a poll request packet for requesting the network management station to send a polling signal instead of automatically sending the unusual events to the management station. When the managed station is polled, it reports the abnormal events to the network management station.
Alarms are specific types of notifications concerning detected faults or abnormal conditions. Information that is included in the alarm is a loss of signal, a power problem, a timing problem, a high/low ambient temperature, high/low humidity, toxic gas, etc. For more information concerning the alarms, reference should be made to a book entitled "SNMP, SNMPv2, and CMIP: The Practical Guide to Network-Management Standards" by William Stallings, published by Addison-Wesley Publishing Company, One Jacob Way, Reading, Mass. 01857, pages 488-492.
The aforesaid related art has encountered the problem in that if the poll request packet is lost during the transmission to the management station, the managed station must resend a poll request after a predetermined time period. This leads to the problem that the collection of the unusual events is undesirably delayed.
What is desired is an improved technique for avoiding the possibility of a long delay in reporting an alarm to the network management station in a wide area network.